[Digestion] Grass clipping digester start up.

[Hoysall Chanakya]

Dear Wayne and Digestion 'Listers' (pun uninteded),
Grass clippings works quite well in a biogas plant.  Try a digester in
which the feed moved horizontally instead of the conventional vertical
movement.  One can reasonably expect a little above 450 litres of biogas
per kg of dry matter added.  Needless to state that there will be about
50-60% degradation in the 30d residence time given for digestion.

When grasses are digested, the digested material will look quite like the
original. However, one can see a lot of sloughed off /digested portions
when the digested material is held against light.  I would suggest that
you choose a continuous digester instead of a batch operated one.

When you do not have dung to start the reactor with, look for a friendly
biogas plant owner and book the digester effluent - about a weeks output
or nearly a sixth to a quarter of the volume of your proposed digester. 
It would start well with such a level of inoculum.  I have started
reactors in the mountains with about 5% of volume as primary inoculum,
left it for a week after diluting with water.  To this one adds the
feedstock but at low rates that is increased gradually.

best wishes
Chahakya


-- 
Center for Sustainable Technologies
Assoc. Faculty. Center for Contemporary Studies
Center for Infrastructure, Sustainable Transport and  Urban Planning,
Indian Institute of Science, Bangalore


> G'day all!
>
> About ten years ago I made a 100 litre test digester that I fed grass
> clippings.  I can't recall starting it up with any manure at all. I also
> don't remember feed rates etc.. ...the whole process was pretty
> unscientific. It did produce a combustible gas however.
>
> Now we are looking at a starting a larger unit that runs on grass
> clippings
> and eventually food waste. We don't have access to manure.  Can someone
> give me pointers on how to get things going? The new unit will be several
> cubic metres. I'd prefer to avoid creating a smelly messy failure if at
> all
> possible.  Your input would be greatly appreciated.
>
> Blessings,
> Wayne
>
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>



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